This invention relates to high density composite ceramic articles formed by integrally assembling two or more molded constituent members of prescribed shape and more particularly high density composite ceramic articles of particularly complicated shape and a method of manufacturing the same.
A molding-sintering process is indispensable to the manufacture of ceramic articles. However, production of high density ceramics requires a long sintering time. The larger a ceramic product, the more extended a molding-sintering period. This process is generally accompanied with the drawbacks that the resultant product is subject to chipping or breakage, and moreover a large scale plant is required. Therefore, the process of molding and sintering a single large ceramic block is not always favorably accepted from the industrial point of view. A Japanese patent disclosure No. 42812, 1972, for example, sets forth a method of manufacturing high density ceramics by hot pressing a low density molding of complicated shape in a powdery pressure-transmitting medium. The disclosure process, however, not only has the drawback that once chipping or breakage occurs in any portion of a product while being molded or sintered, the product is disqualified for commercial acceptance, but also is not well adapted for tonnage manufacture of large ceramics.
To avoid the above-mentioned difficulties, another method of previously molding two or more constituent members and finally integrally assembling them into a product has been proposed as an attempt to provide ceramics of relatively large size or complicated shape by an industrially advantageous process.
For example, a Japanese patent disclosure No. 75910, 1974 which points out the difficulty of hot pressing ceramics of complicated shape with a great mechanical strength sets forth a method of producing, for example, a composite ceramic turbine rotor by fabricating the wing portions by casting, ordinary sintering and bonding reaction, separately hot pressing the hub portion and finally integrally assembling said wing portions and hub portion by refractory cement.
Generally, a turbine rotor is rotated at as high a speed of more than 60,000 r.p.m. and subjected to a tensile force acting in the circumferential, as well as, radial direction, and moreover thermal stress is present. While the turbine rotor is operated, the tips of the wing portions are heated to a temperature as high as 1100.degree. to 1200.degree. C. Therefore, the turbine rotor is required to have a sufficient mechanical strength to withstand such high temperature.
However, according to the manufacturing method proposed by the aforesaid Japanese patent disclosure No. 75910, 1974, a turbine rotor has the joints bonded by refractory cement and is likely to cause irregularities to occur in the density of both blade portions and hub portion or in the whole structure, failing to display high mechanical strength as expected.